1. Field of the Invention
This invention relates in general to engines for converting energy into torque and particularly to a new and useful internal ballistic engine which incorporates an internal ballistic piston for accumulating a portion of the internal energy as kinetic energy and an energy accumulating chamber for momentarily accumulating the kinetic energy of the piston in the form of potential energy and releasing the energy to produce a torque on a shaft.
2. Description of the Prior Art
One of the most widely used engines for converting energy into a usable torque is of the internal combustion type which utilizes a cylinder having a closed end with one or more valves adjacent the closed end and having a reciprocating piston within the cylinder. Combustible fluid and air is injected or drawn into the cylinder space above the piston and then compressed. After compression the fluid and air are caused to ignite, either through the use of a spark plug or, in the case of a diesel engine, by the heat produced in the compression stroke and work is produced when the piston is forced downward in the cylinder due to the expanding gases which are products of combustion from the fluid and air mixture.
The piston is in general connected to a rotating crankshaft which is given torque by the action of the pressure inside the cylinder. During combustion of the fuel, which in the conventional piston engines may last for a few degrees of rotation of the crankshaft at low engine speed to over 50 degrees of rotation at high speeds, the gases inside the cylinder above the piston become highly energized due to the combustion process.
The temperature and pressure of the gases increase to a value greatly above the ambient conditions around the cylinder. Gas temperatures on the order of 5,000 degrees coupled with pressures of about 1,000 psi are usual. Due to the high differential between the energy states within the cylinder and outside the cylinder substantial loss of energy occurs in the form of heat flowing from the hot gases to the cylinder wall. This heat is eventually lost to the cooling system which is provided for this purpose. This loss of heat lowers the temperature and pressure of the hot gases and therefore reduces the amount of available work which can be provided to the crankshaft.
Concurrently with this loss of energy, the motion of the piston during expansion corresponds to an increase in the volume of hot gases. This volume increase represents work transferred by the gases to the piston. The amount of work done, measured in foot-pounds, is equal to the products of the volume increase multiplied by the pressure of the gases at the time of this increase. Performance of this work represents a conversion of heat energy into mechanical energy and as the expanding gases do this work, their temperature and pressure is further lowered. The energy thus dissipated in each of the above processes will diminish the rate at which the other process dissipates its energy.
Because of the nearly sinusoidal motion of the pistons in the conventional piston engines, due to their direct engagement with the crankshaft, the pistons move at relatively low velocity while in the vicinity of TDC (Top Dead Center), while the temperature of the gas inside the cylinder remains high. As the heat losses to the wall of the cylinder are proportional to the difference in temperature between gas and wall and also proportional to the time the piston stays around TDC, the heat losses in the conventional piston engines, due to conduction and radiation, while the piston remains in the vicinity of TDC are high. It has been shown using a computer that at 1000 r.p.m. as much as 35% of the heat in the fuel can be lost to the wall of the cylinder while the piston remains within .+-.15.degree. from TDC.
It is apparent that if the piston is allowed to move freely, especially during the early phase of expansion in the gases, the fast expansion of the chamber would cause quick reduction of temperature and pressure resulting in a lower amount of heat lost by conduction through the chamber walls and therefore allowing a larger amount of thermal energy to be available for providing the useful work. When the piston is freed from direct engagement with the crankshaft, its motion is determined in accordance with ballistic principles based on its mass and the forces applied to it. A gun, for example, representing the most rudimentary form of internal combustion engine, converts heat into work with a very high degree of thermal efficiency because the bullet in the barrel is free to accelerate, being restricted only by its own mass and friction with the barrel wall. The motion of the bullet conforms to ballistic principles. The gun, in effect, corresponds to an engine having an exceedingly high compression ratio, allowing more energy to be converted into work before the bullet leaves the barrel.
The compression ratio of an internal combustion engine is the largest volume of the combustion chamber divided by the smallest volume of the combustion chamber as determined by the moving piston therein, for example, as in the case of a bullet in the barrel, the volume of the barrel divided by the volume of the bullet casing containing propellant. This ratio is indicative of thermal efficiency also in all internal combustion engines.
The conventional engines can be designed to operate with compression ratios around 8.5:1. At higher compression ratios and despite the high octane fuels used, detonation of the fuel mixture takes place, known as "knocking." During detonation the velocity of the flame front is greatly increased causing almost instantaneous conversion of the fuel to heat. As the piston is moving very slowly at TDC the heat loss to the walls of the combustion chamber is sharply increased with the likelyhood of severe damage to the piston, the heat dissipation of which is limited. In the engine providing a ballistic piston, according to the present invention, quick expansion of the combustion chamber quickly reduces the temperature of the gas in the chamber, thus lowering the rate of heat loss so that even detonation of the gas will have no harmful effect on the engine. The internal ballistic engine will be able to operate at higher compression ratios, a property which will further increase the thermal efficiency of engines. Another consequence of the quick expansion of the combustion chamber via a ballistic piston is the facility of using highly flammable low octane fuels for increasing the rate of burning of the fuel around TDC for greater thermal efficiency.